Synchronization of AC power sources

Synchronization is a process involved in connecting two AC power supplies. AC power sources

such as transformers and generators need to be operated in parallel. This may be requiredfor greater reliability and capacity sharing.

In the picture, the incoming power source, a generator(#1) is being synchronized with a busbar which is already to a generator(#2) which is running.For synchronizing three conditions need to be satisfied1. Equal VoltagesBy Equal voltages, we mean that the rms value of the voltages should be equal.

2. Equal frequenciesEqual frequencies implies that the two sources should have equal frequencies. A 50Hz sourcecan only be synchronized with another source whose frequency is also 50 Hz.

3. Same Phase SequenceThe sources should have similar phase sequence i.e. RYB and RYB or RBY and RBY.

4. Same Phase angleThe vectors of the two sources should have the same phase angle.

It is possible to bring the frequency, phase angle and voltage within synchronizing limits by adjusting the speed and voltage of the generator.

The circuit breaker connecting the two power sources can be closed when all these conditions are satisfied. The drawing shows vector diagrams of two three phase voltages whose phase sequences, phase angles, voltages and frequencies are equal

Special equipment and checks are used to ensure that the above conditions are satisfied.